550 R. W. Hegj-ier 



fresh egg. Eggs centrifuged when in the blastoderm stage or 

 older almost always produce normal embryos and sometimes 

 larvae. 



10 Centrifugal force has no influence upon the rate of develop- 

 ment of eggs which produce normal embryos or larvae. 



1 1 The orientation of the embryos produced by centrifuged 

 eggs is not affected by centrifugal force. Dwarf embryos, how- 

 ever, are frequently formed at the posterior ends of the eggs; these 

 never produce larv«. 



12 In the majority of cases the eggs laid by centrifuged beetles 

 produce normal larvae. 



13 The eggs of insects, although supposed by many embryol- 

 ogists to be the most highly organized of any animal eggs, may 

 have their contents profoundly disturbed without preventing the 

 production of a normal embryo. The cytoplasm and nuclei of 

 centrifuged eggs are forced out of their usual positions, but often 

 normal development takes place. This would indicate that a 

 high degree of organization does not prevent the egg from adapt- 

 ing itself to changed conditions. 



The University of Michigan. 

 February 19, 1909. 



LITERATURE 



Andrews, F. M. '03 — Die Wirkung der Centrifugalkraft auf Pflanzen. Jahrb. 



wiss. Bot., Bd. 38. 

 Born, E. '85 — Biologische Untersuchungen. I. Ueber den Einfluss der Schwere 



auf das Froschei. Arch. f. mikr. Anat., Bd. 24. 

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 Ges. zu. Wiirzburg, N. F., Bd. 34. 

 '01, h — Die Polaritat von Ovocyte, Ei und Larve des Strongylocentrotus 

 lividus. Zool. Jabrb. Abth. f. Anat. u. Ontog., Bd. 14, Heft 4. 

 BuMPUS, H. C. '91 — The Embryologyof the American Lobster. Journ.of Morph., 



vol. 5. 

 CoNKLiN, E. G. '05 a — Organ-forming Substances in the Eggs of Ascidians. Biol. 

 Bull., vol. 8. 

 '05 b — Mosaic Development in Ascidian Eggs. Journ. Exp. Zool., vol. 2. 

 '08— The Mechanism of Heredity. Science, N. S., vol. 27. 



